The six-strong gang used the religious dress to disguise themselves and the tools they were carrying, police said.

The axe and sledge hammer-wielding group smashed glass cabinets at a pre-arranged moment then filled holdalls with the watches during the 8.30pm raid.

Stunned onlookers in Oxford Street, the capital's busiest shopping district, watched as the gang met accomplices outside in getaway vehicles believed to be a moped, two motorbikes and a black BMW estate.

Detective Chief Inspector Andy Noyes, from the Flying Squad, said: "This was a brazen attack that was clearly well planned and well thought through. Fortunately robberies like this are rare.

"I'd like to thank those members of the public who stepped in and detained our two suspects. "Their quick thinking and brave actions have helped our investigation.

"We have recovered a number of items from the scene, as well as the gang's vehicles they used in their escape and we are carrying out a full forensic examination.

"Extra officers are in the Oxford Street area and our investigation is moving quickly with a number of lines of enquiry. We still want to hear from anyone who saw the robbery, who may have seen the vehicles involved in the time running up to or after the robbery or who think they may know who has been involved."

A 19-year-old man has been charged with offences relating to the robbery, police said.

A 24-year-old man, was taken to a central London hospital, believed to be suffering from a fractured leg. He remains in hospital.

The two motorbikes were recovered by police in Bolton Place, near the junction with Taunton Place, NW1. The suspects were seen to run off in the direction of Russmore Road, NW1, where another vehicle may have been waiting.